Discussion:
In this study, we evaluated sequence divergence and incidence of
recombination in three major endosymbionts (Wolbachia ,Cardinium and Arsenophonus ) to answer whether the
ecological community that they are a part of is the primary seat of
their horizontal transfer and diversification. We used soil arthropod
community because it is relatively insular and has a relatively high
habitat endemicity of the residents. Our main goal was to assess whether
community members facilitate the spread of endosymbionts as they
themselves come in contact with each other for various ecological
interactions. To properly assess whether ecological communities are
indeed the seat of endosymbiont transfer and diversification, one needed
to compare multi-gene phylogenies of such endosymbiont surveys from
different communities. However, in spite our extensive literature
surveys we could not find any such previous reports. Most surveys of
arthropod communities concentrated on the hosts rather than on their
endosymbionts (Gonçalves, Pereira, & Liu, 2012). Some studies like
Kittayapong et al. (2003) and Sintupachee et al. (2006) did uncover the
resident endosymbionts but mostly with single genes. This precluded a
cogent comparison of endosymbiont diversity and incidence of
recombination with the present study. Another set of studies did indeed
sample endosymbionts with multi-gene sequences but concentrated on a
few, and not all, host taxa within a community (Bing et al., 2014).
Again, such studies are not ideal comparisons with the present one as
these were biased towards a few host taxa. To partially overcome this
problem, we used statistical models with extensive resampling. We
observed that the supergroup A Wolbachia infections andCardinium do indeed show less pairwise divergence, than expected,
in accordance with our predictions. However, supergroup BWolbachia and Arsenophonus infections did not show this
pattern. In fact, the former shows more variation than expected whereasArsenophonus shows no significant difference. This indicates that
these endosymbionts have different propensity and/or rates of horizontal
transfer within the community. We speculate what can be the reasons
behind this.